Ammonia converter



Jan. 6, 1970 H. c. HERP, JR

AMMONIA CONVERTER 2 Sheets-Sheet 1 Filed May 11, 1964 INVENTOR. HENRY C.HERP J I (xiii ATTORNEYS Jan. 6, 1970 Filed May ll, 1964 v H. C. HERP,JR

AMMONIA CONVERTER 2 Sheets-Sheet 2 INVENTOR. ENY C. HERP J ATTORNEYSUnited States Patent 3,488,161 AMMONIA CONVERTER Henry C. Herp, Jr.,Louisville, Ky., assignor to Girdler Corporation, Louisville, Ky., acorporation of Ohio Filed May 11, 1964, Ser. No. 366,314 Int. Cl. B01j9/00 U.S. Cl. 23-289 11 Claims ABSTRACT OF THE DISCLOSURE A catalyticconverter with an inner sleeve joined to the top closure, and a catalystbasket supported within the sleeve. The closures are hemispherical andthinner than the casing, and welded thereto, permitting ease of cuttingand rewelding.

The invention relates to an ammonia converter, and more particularly toa form of ammonia converter which may be connected in parallel to aplurality of similar converters, whereby a range of capacities may beachieved.

In the usual process for the manufacture of ammonia, ammonia synthesisgas containing hydrogen and nitrogen in the desired proportions, iscompressed to approximately 5000 p.s.i.g. The compressed synthesis gasis combined with a recycle stream in a ratio of about 4 parts of recyclegas to 1 part synthesis gas. The combined gas stream is filtered toremove compressor oil and the like, cooled by heat exchange, and furthercooled by refrigeration so as to condense ammonia in the gas stream. Theliquid ammonia is separated from the gas stream in a secondary ammoniaseparator and transferred to a flash drum. The gas steam is reheated byheat exchange and caused to pass into an ammonia converter. Within theconverter a reaction takes place which may be represented as follows:

In its usual form, an ammonia converter comprises an elongated,vertically oriented pressure vessel containing (from top to bottom) aheater, a catalyst basket, and a heat exchanger. Synthesis gas isintroduced into the pressure vessel near its top and caused to traveldownwardly between the inside surface of the vessel and the outsidesurfaces of the housings of the elements mentioned above. Thus, theincoming synthesis gas is used to cool the walls of the pressure vessel.Near the bottom of the vessel, the gas is introduced into the lowerportion of the heat exchanger where it is caused to pass about aplurality of tubes carrying the downwardly flowing product gas. Thesynthesis gas is then caused to flow upwardly through a complex bafileassembly located between the heat exchanger and the catalyst basket. Thebaflle assembly directs the synthesis gas upwardly through the catalystcooling tubes which extend through the catalyst basket. The catalystcooling tubes lead to a passage which in turn conducts the synthesis gasto the upper portion of the startup heater means. At this point, thesynthesis gas begins to flow through the heating element into thecatalyst basket. Within the catalyst basket, an exothermic reactionbetween the hydrogen and the nitrogen 3,488,161 Patented Jan. 6, 1970takes place in accordance with the formula above to form ammonia. Aconversion of approximately 20% is obtained. The hot converted gas isthen caused to enter other portions of the above mentioned baffieassembly by which it is led to a plurality of heat exchanger tubesextending the length of the heat exchanger. At this point, the convertedgas is collected and passes out of the converter through an outlet atits bottom. The converted gas is then cooled, and then caused to enteran ammonia separator. The gas recovered in the separator may be recycledas mentioned above.

Ammonia converters of the type described are large, complex structures.The pressure vessel is necessarily thick-walled and often provided withexpensive highpressure fianged closures which occasionally give troubledue to leakage. Such converters require heavy type fabrication, aredifficult to ship, and require a great deal of time and expense tomanufacture. Furthermore, such converters often require individualdesigning to meet the production requirements of the particularinstallation of which they are to be a part.

It is therefore a primary object of the present invention to provide anammonia converter, of a given capacity, which is adapted to be connectedin parallel to a plurality of similar converters whereby a range ofcapacities may be achieved.

It is an object of the present invention to provide an ammonia convertercharacterized by greatly simplified fabrication. The converter of thepresent invention is comprised of a number of standard sections made upof pipe, castings, pressed heads, tubes and thin plates, obviating thenecessity of heavy type fabrication.

It is an object of the present invention to provide an ammonia converterwhich would required one-half or less the time required to fabricate theusual converter, and which would be easier to ship than the usual large,heavy-walled converter.

It is an object of the present invention to provide an ammonia converterof an all-welded design, eliminating expensive high-pressure flangedclosures. If such closures were to be eliminated on large diameterthick-walled vessels, cutting and re-weldin to change catalyst or tomake repairs would be a major undertaking requiring considerable downtime. The converter of the present invention, is so constructed as tomake such cutting and re-welding feasible, with the resultantelimination of flanged closures and the change of leakage at suchclosures.

It is an object of the present invention to provide an ammonia converterof a simplified and improved design, including a simplified method ofjoining the catalyst section to the heat exchanger section.

It is an object of the present invention to provide an ammonia convertercharacterized by the maximum use of the converter cross-section for heatexchanger tubes.

It is an object of the present invention to provide an ammonia convertercharacterized by a small catalyst volume relative to the outer shellmass, and the use of catalyst cooling gas to blanket the catalyst bed.This design enables the catalyst bed to be properly cooled, andeliminates the necessity of insulation around the catalyst bed whileinsuring that the outer shell of the converter will be sufiicientlyprotected against high temperature.

These and other objects of the invention which will be describedhereinafter, or which will be apparent to one skilled in the art uponreading this specification, are accomplished by that structure andarrangement of parts of which contain exemplary embodiments will now bedescribed. Reference is made to the drawings wherein:

FIGURE 1 is a diagrammatic representation of a plurality of the ammoniaconverters of the present invention connected in parallel.

FIGURE 2 is an elevational cross-section of the converter of the presentinvention.

FIGURE 3 is a cross-sectional view of the converter taken along thesection line 33 of FIGURE 2.

FIGURE 4 is a cross-sectional view of the converter taken along thesection line 44 of FIGURE 2.

FIGURE 5 is a partial elevational view, in cross-section, illustratinganother form of heat exchanger for the converter of the presentinvention.

The converter of the present invention is best shown in FIGURE 2. Theconverter comprises a shell 1 of reduced thickness at its ends as at 2.The ends of the shell are closed by hemispherical heads 3 and 4, whichmay be pressed from metal plate. Since the heads are hemispherical inconfiguration, their thickness need only be approximately half thethickness of the cylindrical outer shell. Within the outer shell, theammonia converter is provided with an inner shell 5 having an outsidediameter slightly less than the inside diameter of the outer shell 1.This difference in diameter provides an annular passage 6 between theOutside surface of the inner shell 5 and the inside surface of the outershell 1. The location of the inner shell, to insure that the passage 6is uniform in width thereabout, may he provided with guide means 7. Theinner shell 5 may be welded or otherwise affixed to the head 3 as at 8,and provided with insulative material 9 at its upper end.

The lower portion of the inner shell 5 comprises a heat exchange sectiongenerally indicated at 10. The heat exchange section comprises a chamberformed by the inner shell and provided with a plurality of heatexchanger tubes 11. The tubes 11 are supported at the bottom of theconverter by a tube sheet 12. The upper ends of the tubes 11 aresupported by a second tube sheet 13. It will be noted that the innershell 5 does not extend down to the tube sheet 12, so that an annularentrance to the heat exchange section is formed between the tube sheet12 and the lower end of the inner shell 5, and is generally indicated at14. Within that portion of the shell 5, constituting the heat exchangersection, a plurality of baflles are located, two of which are indicatedat 15 and 16. These bafiies are horizontally oriented, and permanentlyaffixed to the tubes 11, or supported by rods from tube sheet 12. Thebafiles are provided with a plurality of perforations through which theheat exchanger tubes 11 extend.

A catalyst basket 17 is located within the upper portion of the innershell 5. The lower portion of the catalyst basket is permanently aflixedto a catalyst support 18, which, in turn, is permanently afiixed to theupper tube sheet 13. The catalyst support 18 may be provided with acatalyst screen 19 to prevent catalyst from passing therethrough. 'Theupper end of the catalyst basket 17 may also be provided with a catalystretaining screen 20, to hold the catalyst in place during shipment andinstallation of the ammonia converter. It will be noted that thecatalyst basket 17 has an outside diameter slightly less than the insidediameter of the shell 5 whereby an annular gas passage 21 is formedtherebetween. Catalyst basket guides 22 may be employed to insure properspacing of the catalyst basket.

FIGURES 3 and 4 illustrate the construction of the upper tube sheet 13and the catalyst support 18. As stated above, these two elements areadapted to be affixed together as by welding or the like (as at 23 inFIG. 2). The co bination of the e two e emen s e iminates th complexbaflie system generally used between the heat exchanger section and thecatalyst basket of an ammonia converter. Referring first to FIGURE 3, itwill be noted that the catalyst support is substantially hexagonal inconfiguration, and provided with a plurality of transverse slots 24constituting gas passages from the catalyst basket. The substantiallyhexagonal configuration of the catalyst support 18 provides gas passages25 between the catalyst support and the inner shell 5. The catalystsupport is also provided with guide surfaces 26 which may bear againstthe inner surface of the shell 5.

FIGURE 4 illustrates the construction of the upper tube sheet. It willbenoted that the upper tube sheet 13 is of the same substantiallyhexagonal configuration as the catalyst support 18, providing for thegas passages 25 between the upper tube sheet and the inner shell 5.Similarly, the upper tube sheet is provided with guide surfaces 27 whichmay bear against the inner surface of the shell 5. The tube sheet 13 isprovided with a plurality of perforations within which the upper ends ofthe heat exchanger tubes 11 are retained in gas-tight fashion.

Referring to FIGURE 2, it will be noted that the catalyst support 18 isprovided with a downwardly extending flange 18a, the lower end of whichis welded to the upper surface of the tube sheet 13 as at 23. Thus, achamber 28 is formed between the catalyst support 18 and the tube sheet13, which are held in spaced relationship by the fiange 18a.

The ammonia converter of the present invention is provided with asynthesis gas inlet 29 in the head 3. A product gas outlet 30 isprovided in the head 4. A start-up heating element 31 may also beprovided in the head 3. The heating element will extend through thehead, the insulation 9 and into the chamber 32 formed by the inner shell5, the catalyst retaining screen 20 and the insulation 9.

A cold gas inlet, or by-pass inlet 33 extends through the head 3 andinsulation 9, into the chamber 32. Finally, the ammonia converter may beprovided with additional elements, as for example a temperatureindicator generally shown at 34. There may be a perforated plate 20aunderlying the screen 20 at the top of the catalyst basket.

Briefly, in the operation of the ammonia converter of the presentinvention, synthesis gas is introduced into the converter via the inlet29. The synthesis gas flows downwardly through the annular passage 6 tothe bottom of the converter and serves as a means for cooling the outershell '1. At the bottom of the converter, the synthesis gas passes intothe heat exchanger section 10 through the annular opening 14. Thesynthesis gas is caused to flow upwardly through the heat exchangersection, around the battles 15 and 16 and the heat exchanger tubes 11.At the top of the heat exchanger section, the gas passes through thepassages 25 formed between the inner shell 5 and the peripheral surfacesof the upper tube sheet 13 and the catalyst support 18. The synthesisgas continues its upward flow in the annular passage 21 to the chamber32. At this point, the synthesis gas enters the catalyst bed through thecatalyst screen 20 and/ or plate 20a and the exothermic reactiondescribed above takes place. The product gases pass out of the catalystbasket through the catalyst retaining screen 19 and the longitudinalslots 24 in the catalyst support 18, and into the chamber 28. From thechamber 28, the product gas enters the heat exchanger tubes 11 and flowsdownwardly therethrough to the converter outlet 30.

When the converter is started up, the incoming synthesis gas may bebrought to reaction temperature by the start-up heater 31. During theoperation of the converter, the reaction temperature of the synthesisgas will be obtained by heat exchange of the upwardly flowing synthesisgas with the downwardly flowing product gas in the heat exchanger tubes11. There will also be heat exchange between the upwardly flowingsynthesis gas and the cata-. lyst basket while the synthesis gas isflowing upwardly through the annular passage 21. This heat exchange willalso serve to maintain the proper temperature within the catalyst bed.

As an additional means of retaining the proper temperature within thecatalyst bed, additional synthesis gas may be introduced through thecold gas or by-pass inlet 33. Synthesis gas so introduced will by-passthe heat exchanger section of the ammonia converter.

FIGURE 5 illustrates an alternate construction for the heat exchangersection of the ammonia converter of the present invention. Like partshave been given like index numerals. In this embodiment, the bafllessuch as those illustrated at 15 and 16 in FIGURE 2 are eliminated, andthe heat exchanger section is packed with an inert material (generallyindicated at a) of approximately the same size as the catalyst used inthe catalyst basket. A screen 35, to retain the inert material, isplaced about the annular opening 14 between the end of the inner shell 5and the tube sheet 12. In this embodiment, the use of the inert materialinsures the proper heat exchange between the upwardly flowing synthesisgas and the heat exchanger tubes 11, and eliminates the necessity andexpense of providing baffles within the heat exchanger section.

As indicated above, a plurality of ammonia converters of the presentinvention may be connected in parallel to provide a product gas outputof substantially any capacity desired. FIGURE 1 illustrates a pluralityof ammonia converters 36 so connected. The synthesis gas inlets 29 areconnected to an inlet header 37. The converter outlets 30 are connectedto an outlet header 38. The cold gas or by-pass inlets 33 are connectedto a by-pass header 39. In this way an installation may be made of anydesired production capacity, or the capacity of an installation may beincreased simply by adding more converters of the type described.

Ammonia converters of the type described may be more easily and lessexpensively fabricated. Similarly, the fabrication may be more quicklyaccomplished. Converters of the type described may be more easilyhandled and shipped. It will further be understood by one skilled in theart, that the ammonia converter of the present invention may beincorporated not only in a vertical position but also in an inclined orhorizontal position. The use of hemispherical heads allows for a reducedthickness of the outer shell at the heads. This in turn permits anall-welded design for the pressure vessel. Expensive and sometimestroublesome flanged closures are eliminated since cutting and reweldingof the thin-walled portion of the converter to change catalyst or makerepairs is easily accomplished with a considerable reduction of downtime.

The use of the converters of this invention connected in parallel asshown in FIGURE 1, is greatly facilitated by the fact that while long,they may be made with a relatively small diameter. Dimensions do notconstitute a limitation on the invention; but in an exemplaryconstruction the converters may be, say, thirty feet in length betweenheads while having an outside diameter of no more than about eightinches. In such a converter the heat exchange section may be about tenfeet in length, and the catalyst basket about twenty feet in length.

Modifications may be made in the ammonia converter of the presentinvention without departing from the spirit of it. For example, when theconverters of the present invention are connected in parallel as inFIGURE 1, the individual start-up heaters 31 for each converter may beeliminated. The individual start-up heaters may be replaced by a singlestart-up heater located in the bypass header 39, serving a bank ofammonia converters. Such a heater is diagrammatically represented at 40in FIG- URE 1.

The invention having been described in certain exemplary embodiments,what is claimed as new and desired to be secured by Letters Patent is:

1, A converter comprising:

(1) a cylindrical casing having top and bottom ends,

(2) closure means at the top and bottom of the eas- (3) an interiorcylindrical sleeve joined to the top closure means and extendingdownwardly within the said casing to a point near the bottom endthereof,

(4) a lower tube plate jointed to the lower closure means and perforatedfor the reception of heat exchange tubes,

(5) an upper tube plate located intermediate the ends of said sleeve andperforated for the reception of heat exchange tubes,

(6) heat exchange tubes extending between the said tube plates andforming a heat exchange section, (7) a perforated catalyst support platemounted above said upper tube plate and spaced therefrom, and joined tosaid upper tube plate by means of a flange whereby to form a chamberbetween said upper tube plate and said perforated catalyst supportplate,

(8) a cylindrical catalyst basket above said catalyst support plate,spaced inwardly from said sleeve, the top of said catalyst basket beingspaced from the upper closure means, there being passageways for gasbetween said upper tube plate, said catalyst support plate and saidflange respectively and the interior surface of said sleeve,

(9) an inlet means through said upper closure means connecting withaspace in said casing outside said sleeve, and

(10) an outlet means in said lower closure means connecting with thespace below said lower tube plate,

whereby process gases introduced through said inlet means can passdownwardly externally of said sleeve and thence upwardly within saidsleeve and around said heat exchange tubes, past said upper tube plate,said catalyst support plate and said catalyst basket to a space abovethe top of said catalyst basket, and thence downwardly through saidcatalyst basket, said catalyst support plate and said heat exchangetubes to the said outlet.

2. The structure claimed in claim 1 wherein said top and bottom closuremeans are in the form of hemispherical members of lesser thickness thanthe thickness of said casing and are welded thereto.

3. The structure claimed in claim 1 wherein said top and bottom closuremeans are in the form of hemispherical members of lesser thickness thanthe thickness of said casing and are welded thereto, upper and lowerportions of said casing being tapered to reduce the thickness of thesaid portions to substantially the same thickness as the upper and lowerclosure means.

4. The structure claimed in claim 3 including baffles within said heatexchange section for bringing the gases traveling upwardly therethroughinto more intimate contact with said heat exchange tubes.

5. The structure claimed in claim 3 including a packing of inertgranular material within said sleeve and surrounding said heat exchangetubes and a cylindrical screen member lying between the lower end ofsaid sleeve and the said lower tube plate and acting to retain saidgranular material in position.

6. The structure claimed in claim 3 wherein the top of the catalystbasket is spaced from the top closure means so as to provide a chamber,and including supplementary inlet means extending through the topclosure means into said chamber for the introduction of process gasesfor temperature control purposes.

7. The structure claimed in claim 6 including a perforated closure plateat the top of said catalyst basket and wherein the perforated catalystsupport plate and the perforated closure plate at the top of thecatalyst basket are each provided wih a wire screening to assist in theretention of granular catalyst in the said catalyst basket.

8. The structure claimed in claim 6 including a heating means extendingthrough said upper closure means and into the last mentioned chamber.

9. The structure claimed in claim 8 including insulating means locatedin said top closure means at the end of said sleeve, and including alsotemperature measuring means extending through said top closure means andsaid insulative means.

10. A structure comprising a plurality of the converters of claim 6 inassembled relationship, the outlet means of said converters, the inletmeans thereof and the said supplementary inlet means being connectedrespectively to separate headers.

11. The structure claimed in claim 10 wherein the header connected tothe said supplementary inlet means incornorates a chamber having heatingmeans therein.

References Cited UNITED STATES PATENTS 9/1933 Jaeger et a1 23288 5/ 1934Lopez 23289 8/ 1944 Rupp et al. 23288.9 11/1958 Worn 23--289 5/1959 DeRycker et a1. 23289 X 8/1962 Christensen 23289 2/1966 Dreyer et al 232899/1966 Christensen 23289 X FOREIGN PATENTS 9/1961 France.

15 JOSEPH SCOVRONEK, Primary Examiner

